1. Field of the Invention
The present invention relates to a venting, self-stopping, aspirating syringe and, more particularly, to a syringe which doesn't require a plunger to be pushed back by blood pressure and which does not require a timely withdrawal of the syringe from an artery.
2. Description of the Prior Art
Syringe type devices are typically used for obtaining blood samples to perform a blood gas analysis. Many such blood gas analyses require the drawing of arterial blood which has a sufficient pressure whereby it will, in and of itself, under normal circumstances, fill a syringe without the necessity of aspirating. For this purpose, a conventional syringe type device simply consists of a plunger positioned within a main tubular body. The plunger is fully inserted into the main tubular body and the hypodermic needle punctures the artery. As blood flows into the syringe body, the plunger is pushed back thereby.
There are a variety of problems associated with the use of such a conventional syringe. First of all, the technician must carefully watch the syringe as it is pushed back to note when the required quantity of blood is withdrawn. At the precisely correct time, the syringe is withdrawn from the artery. This requirement for precise timing requires a good deal of skill on the part of the technician.
Furthermore, in obtaining blood samples, it is necessary to use an anti-coagulant to maintain the integrity of the blood sample. Typically, a dilute heparin solution has been placed within the syringe body prior to use, filling the syringe. As the plunger is pushed into the body to expel the liquid heparin, a small quantity, approximately 1/4 cc, remains in the syringe, in the area between the end of the plunger and the tip of the hypodermic needle. Therefore, when such a syringe is used to obtain a blood sample to perform a blood gas analysis, the 1/4 cc of liquid heparin remains in the syringe. This small amount of heparin represents a contaminant and diluent which interfers with accurate blood gas analysis values and other chemical evaluations.
As a result of the above problems in the use of conventional syringes for obtaining blood samples to perform a blood gas analysis, several syringe devices have been developed to obtain contaminant-free blood samples. An example of such a device is shown in U.S. Pat. No. 4,257,426 to Bailey. In the Bailey patent, a syringe device includes a main tubular body, one end of which slidably receives a combination sealing member and hollow plunger, with the plunger being rotatably connected to the sealing member. The sealing member has several circular lips so that contact sufficient to create a seal exists between the lips on the sealing member and the syringe body. The sealing member has a lateral vent between several of the lips. A flexible thread fixed to the plunger selectively crosses the lips and breaches the seal created by the sealing member to establish communication between the interior of the plunger and the interior of the tubular body via the lateral vent in the sealing member. Removal of the thread allows a seal to be restored so that a gas-free blood sample can be isolated in the hollow tubular body. Crystalline heparin flakes are placed in the body, eliminating the necessity for liquid heparin.
The Bailey syringe has a variety of advantages over a conventional syringe. Initially, through the use of crystalline heparin, the use of liquid heparin can be eliminated, making blood gas analyses more accurate. Secondly, because of the venting action of the plunger, the position of the plunger can be preset so that as the blood rushes into the syringe body, the air crosses the lips, around the flexible thread. As soon as the blood passes the first series of lips, the syringe is removed from the patient and the plunger is rotated, removing the thread from the seal lips, restoring the seal so that the blood sample can be isolated in the hollow tubular body.
While the syringe of the Bailey patent solves some problems associated with conventional syringes, it creates a new set of problems. That is, since the flexible thread extends across the seal lips and breaches the seal created by the sealing member, blood, as well as air, can flow past the sealing member. Accordingly, proper operation of the device still requires removal of the needle at a precise time from the patient. If the syringe is not removed at the precisely correct time, the blood flows past the sealing member and enters the syringe body, on the backside of the sealing member. Then, when the syringe is removed and inverted, this blood escapes.
Furthermore, the use of the syringe of the Bailey patent requires the technician to learn an entirely new procedure, that of rotating the plunger relative to the sealing member to withdraw the thread. In view of the number of technicians which draw blood, this additional training to use the product properly is a significant disadvantage, especially when the operation of the device is not at all apparent from an inspection thereof.